I’m thinking of buying a hybrid RAV4 and wondered whether the roof will support a fibreglass roof top tent, weighing about 70kgs, if it were to be driven on dirt, possibly corrugated roads? The roof racks don’t appear very strong.
It appears that the RAV4 Hybrid's roof racks can stand up to 80kg, so you should be safe.
According to an American-market RAV4 forum, that is the maximum rating for when the car is moving, as the bars must be able to withstand a sudden change in direction at speed, such as to avoid hitting an animal on the road. The forum adds that, when stationary only, the roof bars can stand up to 270kg.